[74.10] A New Data System for the San Fernando Observatory Video Spectra-Spectroheliograph

S. R. Walton, G. A. Chapman (San Fernando Obs., CSUN)

The San Fernando Observatory Video Spectra-Spectroheliograph (SFO VSSHG) has been
used for observation of vector magnetic fields on the Sun for the last several
years, and was described in Walton and Chapman (1996), Solar Phys. 166, 267. The current VSSHG camera is a commercial video format (512 by 480)
CCD camera from which spectra are recorded on analog 3/4'' professional grade
videocasettes. Recently, commercial off-the-shelf hardware has become available
which can equal the high speed and capacity of this system in a pure digital
mode. We are developing a new data system for the VSSHG consisting of a 1024
square digital CCD camera capable of 15 frames per second, an Intel Pentium-II
based personal computer with fast-wide SCSI hard disk, and a DLT-7000 digital
linear tape drive. This combination of off-the-shelf hardware, purchased for
about $30,000, should achieve the data rate of 7.5 megabytes per second (MB/s)
required for recording 5 frames per second from the CCD camera to the hard disk
in real time, which is sufficient for the VSSHG. The DLT tape drive can record
35 gigabytes at a rate of 5 MB/s uncompressed, and a small amount of data
compression should allow it to record spectra in real time as well. As of this
writing, only the computer has been received, but preliminary tests show that
its hard disk performs at speeds well over 10 MB/s with no special
optimizations. We will take delivery on the camera soon, and hope to have the
first images with the new camera early this winter. A detailed description of
the data system and on-line processing algorithms will be presented.